It is known design practice to calculate indicated mean effective pressure (IMEP) for an internal combustion piston engine using measured in-cylinder pressure obtained with an in-cylinder pressure sensor. The sensor provides cylinder pressure data at various crank angles. As described by Haywood in a publication entitled "Internal Combustion Engine Fundamentals" (1988, p.715), IMEP is a measure of the amount of work delivered to the piston during the compression and expansion stroke for each cycle per unit displaced volume. This information is used to establish optimum valve timing, air/fuel ratio, and optimum exhaust gas recirculation to achieve increased fuel economy and reduced emissions. The use of in-cylinder pressure sensors in this way for high volume production applications is costly, however, because the pressure sensors themselves are expensive. Further, locating the sensors in the cylinder is difficult and each cylinder requires its own sensor.
The calculation of indicated mean effective pressure for production engine applications using such pressure sensor data requires engine control microprocessors with substantial processing power and speed. Further, such control methods are characterized by sensor degradation and variability in system components.